Providing electricity through photovoltaic cells is becoming more popular as this technology has decreased in cost and reliance on other sources of electric power is increasingly disfavored for environmental and strategic reasons. However, providing a general use tile with electrical components that is easy to install and electrically connectable to other tiles without external wiring has been elusive.
Photovoltaics refer to cells that convert sunlight directly into electrical energy. The electricity produced is direct current that can be used as direct current, converted to alternating current through the use of an inverter, or stored for later use in a battery. Conceptually, in its simplest form, a photovoltaic device is a solar-powered battery whose only consumable is light. Because sunlight is universally available, photovoltaic devices have many advantages over traditional power sources. Photovoltaic systems are modular, and so their electrical power output can be engineered for virtually any application. Moreover, incremental power additions are easily accommodated in photovoltaic systems, unlike more conventional approaches such as fossil or nuclear fuel, which require multi-megawatt plants to be economically feasible.
Although photovoltaic cells come in a variety of forms, the most common structure is a semiconductor material into which a large-area diode, or p-n junction, has been formed. In terms of basic function, electrical current is taken from the device through a contact structure on the front that allows the sunlight to enter the solar cell and a contact on the back that completes the circuit.
In the field of solar PV modules, proposals have been made to form the PV module having the general characteristics of a roofing tile so that the PV laminate may be integrated into a roof, commonly but not exclusively, a tile roof. An alternative approach is to have a module which is adapted to be mounted over a roof. However, important considerations to the design and development of PV modules include the ability of the modules to be effectively integrated architecturally into a roof design.
Traditionally a photovoltaic (PV) module is mounted onto a finished rooftop, e.g. a rooftop already covered with shingles or tiles. Installation usually requires the addition of brackets or other devices to which the modules are affixed that require a number of rooftop penetrations to provide anchoring. In some cases existing rooftop material is removed or reinstalled to accommodate the installation. This installation represents additional cost, and in many cases, substantial cost due to the special nature of the installation and the requirement for specially trained installers. Installation can represent 25-30% of the total installed system cost which limits widespread economic viability of PV in the residential and light commercial markets today. In addition to the high cost of installation, PV installation adversely affects the appearance of a rooftop since the “look and feel” of traditional PV modules with metal frames and glass surfaces is discontinuous with other roofing materials. Aesthetics is critical to home builders and home buyers alike.
There have been several attempts to define the PV module as an integrated building material. Most notably, an a-Si on stainless steel product has been promoted as an integrated photovoltaic solution. However, this product has had limited growth due to the use of a plastic coating instead of glass and the overall low efficiency and high cost/Watt of the product.
There have also been attempts to laminate thin film and Monocrystalline Si PV onto various types of tiles that are then used as roofing materials. These products have not succeeded in the marketplace for several reasons including high cost and the large numbers of interconnections needed. Most recently, a product has been designed to replace concrete tiles. Although the form factor and method of installation is consistent with a concrete roofing tile, it still uses a metal frame. While this product looks more aesthetically pleasing than traditional modules and has made some inroads with builders, it still requires specially trained installers and is limited to replacing concrete tiles. No one has come up with a blend of photovoltaics and roofing material that can meet the necessary cost, and material compatibility.
Accordingly, there is still a need for a photovoltaic solar roof or solar facade that does not require special roofing preparation and doesn't impact roofing stability. Furthermore, it is desired that the laying and repair of a solar roof or solar facade may be undertaken, without the expenditure of further cost, and simple to install by normal building trades requiring only a minimum of special training.